[Harp-L] what makes a mic prone to feedback?

[Garry Hodgson <garry@xxxxxxxxxxxx>]

in the recent discussions of mics, several people commented
on this mic or that being resistant to feedback.  that got me 
curious as to what aspects of a mic's design contribute to this.
impedance?  shape?  pickup pattern (omni vs. cardioid)?  
element type?  is it all black magic, or is this well understood?
if the latter, what are the tradeoffs a designer makes?   i.e. what
does he give up for feedback resistance, or what does he get
that would be worth a feedback prone mic?


----
Garry Hodgson, Technical Consultant, AT&T Labs

do for others with no desire of return.
we should all plant some trees
we will never sit under.